Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$26.55	8.857%	$28.9015	$28.90	$28.90	$28.90
Purchase #2	$29.74	7.367%	$31.9309	$31.93	$31.95	$31.90
Purchase #3	$224.93	13.572%	$255.4575	$255.46	$255.45	$255.50
Purchase #4	$200.89	10.418%	$221.8187	$221.82	$221.80	$221.80
Purchase #5	$224.66	6.145%	$238.4654	$238.47	$238.45	$238.50
Purchase #6	$126.59	5.480%	$133.5271	$133.53	$133.55	$133.50
Purchase #7	$212.57	8.415%	$230.4578	$230.46	$230.45	$230.50
7 purchase totals =	$1,045.93		$1,140.5589	$1,140.57	$1,140.55	$1,140.60